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    <script>
        // 链式操作
        // 想终端promise链条执行 -  在返回值位置 返回一个状态为pending的promise
        new Promise((res, rej) => {
            res('ok');
        }).then(val => {
            console.log(val);
        }).then(val => {
            console.log(val);
            return new Promise(() => {});
        }).then(val => {
            console.log(val);
        }).then(val => {
            console.log(val);
        }).then(val => {
            console.log(val);
        })
    </script>
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